mstrens wrote: ↑Mon Apr 24, 2017 5:35 pm
indeed , if you have
#define REFERENCE_VOLTAGE 5026
then you should use scale
1000*1023/5026 = 203.54
If #define REFERENCE_VOLTAGE is set as comment, then oXs supposes that Vcc = 5000.
If you only measures NTC, in fact the value for reference voltage does not matter because arduino ADC will return the same value for different Vcc (arduino ADC and NTC voltage are both ratiometric).
REFERENCE_VOLTAGE play a role when you want to measure an abolute voltage (like a lipo).
Ok, using this calculation, and those are my actual values, the scaling seems to be NOT correct.
I just had a chance to run one of my engines with an NTC installed on the cylinder head, near the base of the glow plug.
At room temperature the reading seems to be quite close. Compared with my temperature measuring gun (chinese, don't know how accurate it is), at 36 degrees, I already noticed a 1 degree difference.
At 100 degrees, the radio displays around 120. At 130 degrees, the radio displays around 170. This is quite a difference. it seems obvious that the higher the temperature, the grater is the difference between radio and temp gun..
I will run some more tests today, but can't start the engine anymore.. too noisy and I don't want to bother my neighbors.. But I can try to heat up the top of the engine with my heat gun, or stick another NTC to a metal plate and heat it up, just for testing..
Any ideas please??
Thank you..
João